DE-U-70 31 718 describes a valve which has in the valve housing a rotating punched disk, with which two different amounts of flush water can be set. To rotate the disk, an upper hood of the valve housing must be taken off. If the drain valve is already mounted in a flush tank, and in particular in the case of a concealed flush tank, this is not possible or hardly so.
From DE-A-34 00 166 a similar drain valve is known in which outside the valve housing a handle is arranged with which the desired flush water quantity is adjustable. Changing the quantity of flush water is indeed possible with this valve, but here too it is necessary to reach comparatively deep into the flush tank.